1. Field of the Invention
The present invention relates to a substrate having a conductive layer such as a wire and an antenna, which is provided in a semiconductor device such as a wireless chip, a wireless tag, a wireless IC, an RFID and an IC tag and used for communicating data bi-directionally and wirelessly, and to a manufacturing method thereof. The invention also relates to a manufacturing method of a semiconductor device having an antenna for communicating data bi-directionally and wirelessly.
2. Description of the Related Art
In recent years, ICs having a function of communicating data wirelessly have been actively developed, such as a wireless tag, an IC tag and a contactless IC card. The IC tag and the contactless IC card require an antenna for communicating data wirelessly. The antenna is formed by embedding a coil of wire, printing, etching of a conductive thin film, plating or the like. Above all, the printing is widely adopted because of its high throughput.
Electromotive force generated when an antenna resonates with a reader/writer depends on number of windings, area and the like of a coil of an antenna, a frequency of electromagnetic wave communicated between an antenna and a reader/writer, and the like. A frequency at which an electromotive force is large is called resonant frequency, which depends on an inductance and a capacitance of a coil. The inductance of a coil depends on a form of the coil, such as size, shape, number of windings, and distance between adjacent coils. In particular, the inductance of a coil is proportional to the length of a coil and inversely proportional to a distance between adjacent coils.
When a print with conductive paste is conducted on a substrate by screen printing, however, the conductive paste filling in an opening of a mask spreads from the opening, which causes overflow. The overflow of the conductive paste from the opening of the mask makes a peripheral region (edge portion) 1602 of a conductive paste 1601 have a small taper angle as shown in a cross sectional view of a conductive paste in FIG. 16A. A conductive layer formed by baking such a conductive paste is short-circuited with an adjacent layer, leading to reduced yield.
Further in screen printing, conductive pastes filling in openings of a mesh mask are connected to each other to be a line paste. Accordingly, a distance 1613 between adjacent conductive pastes differs, as shown in a top plan view of a conductive paste in FIG. 16B, between a region 1611 of a paste filling in an opening and regions 1612 of the paste connecting to the region 1611. When a conductive layer is formed by baking such conductive pastes to be used as an antenna, the inductance of the antenna is different from that in the case that a distance between adjacent conductive pastes is constant, and lower resonant frequency is obtained, leading to lower electromotive force.
In the regions 1612 with a narrow line width of the conductive paste, the conductive paste is easily separated, which results in lower yield. In addition, depending on the viscosity of the conductive paste, resistance increases because of the thinness of the conductive layer. Several times of prints of conductive paste may be conducted in order to avoid such problems; however, in this case, the number of steps increases and adjacent conductive pastes are connected to each other, which causes a short circuit of conductive layers formed later.